In many liquid crystal display devices that display color images, three subpixels into which one pixel is divided are provided with color filters that transmit red (R), green (G), and blue (B) lights, respectively. However, since approximately ⅔ of backlight with which a liquid crystal panel is illuminated is absorbed by the color filters, a color-filter liquid crystal display device is undesirably low in light use efficiency. Given these circumstances, attention is drawn to a field-sequential liquid crystal display device that performs a color display without use of color filters.
In a typical field-sequential liquid crystal display device, one frame period, i.e. a period of display of one screen, is divided into three field periods, i.e. first, second, and third field periods (these “field periods” being also referred to as “subframe periods”). A color image is displayed on the liquid crystal panel by illuminating the liquid crystal panel with red, green, and blue light-source lights from behind during these first, second, and third field periods and by displaying, during the first field period, a red image corresponding to a red component of an input image signal, displaying, during the second field period, a green image corresponding to a green component of the input image signal, and displaying, during the third field period, a blue image corresponding to a blue component of the input image signal (such a field sequential system being hereinafter referred to as “simple RGB subframe system”). Such a field-sequential liquid crystal display device no longer requires color filters and is therefore higher in light use efficiency than a color-filter liquid crystal display device.
In a field-sequential display device, however, when an observer's line of sight moves within the display screen, shifts in the lighting timings of primary colors of light sources are recognized by the observer, with the result that the color of each field (each subframe) appears to be separate (this phenomenon being called “color breakup”). A known method for suppressing color breakup is a method by which at least one of the red, green, and blue components is displayed in two or more fields during one frame period. For example, in a field-sequential display device in which one frame period includes white, red, green, and blue field periods during which a white image, a red image, a green image, and a blue image are displayed, respectively, an image represented by an input image signal includes, as a red component, a red image that is displayed during the red and white field periods, as a green component, a green image that is displayed during the green and white field periods, and, as a blue component, a blue image that is displayed during the blue and white field periods (such a field sequential system being hereinafter referred to as “RGB+W subframe system”).
Thought is given here to a case where a field-sequential liquid crystal display panel performs a maximum white display. In a simple RGB subframe display device, in this case, as shown in FIG. 23(A), during any of the red, green, and blue subframe periods, the transmittance of a corresponding pixel (optically-modulated pixel) of the liquid crystal panel is at its maximum, so that all of the light from the light source is used for the display. On the other hand, in an RGB+W subframe liquid crystal display device, as shown in FIG. 23(B), the transmittance of the optically-modulated pixel is at its maximum during the white subframe period, and during the red, green, and blue subframe periods, the light source emits light but the optically-modulated pixel enters a nontransparent state. For this reason, the RGB+W subframe system, when employed in a field-sequential liquid crystal display device, undesirably consumes more power than the simple RGB subframe system does.
In conjunction with the invention set forth in the present application, PTL 1, listed below, discloses a color liquid crystal display device that performs one frame display in fields of three primary colors and a field of a white color obtained by mixing the three primary colors. This color liquid crystal display device is intended to reduce power consumption while suppressing color breakup, and is configured to generate a display signal in the white field on the basis of a value obtained by dividing the minimum value Wmin of luminance per pixel in one frame of a three primary color signal that is inputted by the maximum value Wmax of the luminance and generate display signals in the fields of the three primary colors by subtracting, from the three primary color signal, a portion that is displayed in the white field.